Fluorine-containing polymers and preparation and use thereof

ABSTRACT

Fluoroalkyl sulfinates were synthesized and used as a source of fluoroalkyl radicals in aqueous emulsion polymerization. The resulting polymers contained a high level of perfluoroalkyl end groups. When fluoroalkyl disulfinates were utilized, the fluoroalkyl moiety and was incorporated in the polymer backbone. These disulfinates act as monomers, yielding fluoropolymers with specific micro structural fragments, derived from the parent perfluoro disulfinate. Novel fluoropolymers can thus be prepared.

This invention relates to fluorine-containing polymers, theirpreparation and use. In another aspect, this invention relates tomethods of free-radical polymerization of ethylenically unsaturatedmonomers, and to the resulting polymers and shaped articles thereof.

Fluorine-containing polymers, or fluoropolymers, are an important classof polymers and include for example, fluoroelastomers andfluoroplastics. Within this class are polymers of high thermal stabilityand usefulness at high temperatures, and extreme toughness andflexibility at very low temperatures. Many of these polymers are almosttotally insoluble in a wide variety of organic solvents, and arechemically inert. Some have extremely low dielectric loss and highdielectric-strength, and most have unique nonadhesive and low-frictionproperties. See, for example, F. W. Billmeyer, Textbook of PolymerScience, 3rd ed., pp 398-403, John Wiley & Sons, New York (1984).

Fluoroelastomers, particularly the copolymers of vinylidene fluoridewith other ethylenically unsaturated halogenated monomers, such ashexafluoropropene, have particular utility in high temperatureapplications, such as seals, gaskets, and linings--see, for example,Brullo, R. A., "Fluoroelastomer Rubber for Automotive Applications,"Automotive Elastomer & Design, June 1985, "Fluoroelastomer Seal UpAutomotive Future," Materials Engineering, October 1988, and"Fluorinated Elastomers," Kirk-Othmer, Encyclopedia of ChemicalTechnology, Vol. 8, pp. 500-515 (3rd ed., John Wiley & Sons, 1979).Fluoroplastics, particularly polychlorotrifluoroethylene,polytetrafluoroethylene, copolymers of tetrafluoroethylene andhexafluoropropylene, and poly(vinylidene fluoride), have numerouselectrical, mechanical, and chemical applications. Fluoroplastics areuseful, for example, in wire, electrical components, seals, solid andlined pipes, and pyroelectric detectors. Polychlorotrifluoroethylene iscompatible with liquid oxygen, and remains tough at cryogenictemperatures. See, for example, "Organic Fluorine Compounds,"Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 11, pp.20, 21,32, 33, 40, 41, 48, 50, 52, 62, 70, 71, John Wiley & Sons, (1980).

Fluorine-containing polymers can be prepared by free-radical initiatedpolymerization of one or more fluorine-containing ethylenicallyunsaturated monomers. Free radicals are typically formed by thedecomposition of a free-radical initiator. Free-radical initiators maybe decomposed by light, heat, high energy radiation, or as a result ofoxidation-reduction reactions. When free radicals are generated in thepresence of free-radical polymerizable ethylenically unsaturatedmonomers, a chain reaction occurs producing polymer. The polymer can beprepared by polymerization of monomers in bulk, in solution, inemulsion, or in suspension. Fluoroelastomers and fluoroplastics arepreferably prepared by aqueous emulsion or suspension polymerizationbecause of the rapid and nearly complete conversion of monomers, easyremoval of the heat of polymerization and ready isolation of thepolymer. Emulsion or suspension polymerization typically involvespolymerizing monomers in an aqueous medium in the presence of aninorganic free-radical initiator system, and surfactant or suspendingagent.

Polymers of low molecular weight can be prepared by polymerizingmonomers in the presence of a chain-transfer agent. Chain-transferagents react with the growing polymer chain. In this reaction, thegrowing polymer chain is terminated and the chain-transfer agent isconverted into a radical. This newly-formed free-radical typically canreact immediately with monomer, thereby initiating the polymerization ofa new polymer chain. Examples of conventional chain-transfer agents arecarbon tetrachloride, acetone, diethyl malonate, and dodecylmercaptan.Chain-transfer activity varies greatly with changes in solvents andmonomers.

In aqueous emulsion or suspension polymerization of fluorine-containingethylenically unsaturated monomer, conventional chain-transfer agentsgenerally can terminate a growing polymer chain but generally do notimmediately react with monomer to initiate a new polymerization. As aresult, the polymerization generally is slow and most polymer chainscontain an ionic end-group due to initiation by ionic radical-initiator,e.g., sulfate radical ion.

Ionic or polar end-groups generally are not desirable because ofdetrimental affects on rheology. U.S. Pat. No. 4,524,197 (Khan) statesthat the presence of acid end-groups detrimentally effects theprocessing characteristics of fluoroelastomers since these groupsincrease the viscosity of the polymer and interfere with curing systems,especially those based on quaternary phosphonium salts.

Ionic or polar end-groups may also reduce the thermal stability ofcertain fluorine-containing polymers. U.S. Pat. No. 4,743,658 (Imbalzanoet al.) states that perfluorinated resins with certain end groups,especially --COF, --CONH₂, and --CF₂ CH₂ OH, can be chemically reactiveand thermally unstable. Such end groups can evolve HF, which isgenerated by the oxidation, hydrolysis, and/or thermal decomposition ofthese end groups.

Polymers with non-ionic end groups can be prepared by the use ofnon-ionic free-radical initiators, e.g., azobisisobutyronitrile orbenzoyl peroxide. However, most non-ionic free-radical initiators aregenerally insoluble in water and are therefore not suitable for aqueousemulsion or suspension polymerization. The employment of water-insolubleinitiators would require the use of organic co-solvents and/or seedlatices produced with water-soluble initiators.

Chang-Ming Hu, Feng-Ling Quing, and Wei-Yuan Huang, J. Org. Chem., 1991,56, 2801-2804, reported that perfluoroalkyl sulfinates dissolved in anorganic solvent such as dimethyl formamide, react smoothly with allyland propargyl halides in the presence of an oxidant, to yield3-(perfluoroalkyl) prop-1-enes or allenes, respectively, in very goodyields. The mechanism of this reaction is believed to be a free radicaladdition-elimination reaction.

Because sulfinates are well known electron donors, a suitable electronacceptor (oxidant) should initiate electron transfer from R_(f) SO₂ Nato generate R_(f) SO₂. radicals and, subsequently, R_(f). radicals. See,for example, Chang-Ming Hu, et al., supra. The oxidants described inHu's paper, were O₂, Ce(SO₄)₂, and ammonium persulfate. Ammoniumpersulfate was said to be the preferred reagent with dimethyl formamide(DMF) as the solvent.

Although it is widely recognized that fluoropolymers with perfluorinatedend groups are more thermally stable and show rheological advantagesover fluoropolymers with ionic end groups, the only described ways toget these perfluorinated end groups is by use of fluorinated peroxidesas initiators, see e.g., U.S. Pat. Nos. 4,654,444 and 4,663,407 (Oka etal.) or by direct fluorination processes on the final polymer, see e.g.,European patent application EP 91107750.1, Ihara, et al. and referencescited therein.

However, perfluoroperoxides are extremely unstable substances and needto be handled in dilute solutions in halogenated solvents such as Freon™113 at low temperature. Besides the fact that the handling of thesesubstances poses a significant hazard, they also require the use oforganic cosolvents (typically Freon™ 113) during the polymerization. Theuse of Freon™ 113 is undesirable because of possible ozone depletion.Also, because of the thermal instability of these perfluoroperoxides,the polymerization should be carried out below room temperature. Thisimposes the expense of cooling equipment.

Direct fluorination of the final polymer, to obtain perfluorinated endgroups, is a cumbersome process requiring highly reactive fluorine gasto be contacted with finely powdered fluoropolymer at elevatedtemperatures for several hours. In addition, unless the backbone isperfluorinated, direct fluorination may also fluorinate the backbonewhich may be undersirable. The degree of fluorination is highlydependant on the polymer particle size, the temperature, the fluorinecontent of the fluorination gas, and the contact time. These parametersare difficult to control reproducibly. Therefore, it is difficult toobtain a uniform degree of fluorination, especially in a factoryenvironment.

Briefly, in one aspect, the present invention provides a method for thepreparation of fluorine-containing polymer comprising polymerizing,under free-radical conditions, an aqueous emulsion or suspension of apolymerizable mixture comprising a fluoroaliphatic-radical containingsulfinate, and an oxidizing agent capable of oxidizing said sulfinate toa sulfonyl radical. Preferably, said oxidizing agent is water soluble.Preferably, said polymerizable mixture comprises fluorine-containingethylenically-unsaturated monomers.

In another aspect, this invention provides a fluorine-containing polymercomprising a fluoroaliphatic group, e.g., fluoroalkyl or fluoroalkylenegroup, derived from a fluoroaliphatic-radical containing sulfinate. Thepolymer backbone chain can contain heteroatoms, e.g., nitrogen atoms.

The polymerization method of this invention can be used to rapidlyprepare fluorine-containing polymers that are easy to process. Preferredoxidizing agents are persulfates, e.g., ammonium persulfate. High yieldsof fluorine-containing polymer with perfluorinated end groups wereobtained when fluoroaliphatic-radical containing sulfinates were used incombination with ammonium persulfate.

The sulfinates are stable salts that can be stored for several months atroom temperature without any appreciable loss of activity. Becausesulfinates and persulfates are very soluble in water, they readily reactwith each other in the aqueous phase of the emulsion or suspension. Theresulting perfluoroalkyl radical that is formed from this reaction ishydrophobic and therefore readily collapses or absorbs onto the micelleor the polymer particles, inducing a rapid polymerization.

The majority of the polymer end-groups formed by the method of thisinvention are fluoroaliphatic, e.g. C_(n) F_(2n+1) and, whenhydrogen-containing monomers are used, hydride, e.g. CF₂ H and CH₃. Verysmall amounts of CH₂ OH (if any) end groups are detected in the finalpolymer. As used herein, "end-group" refers to groups at the end of thepolymer chain or at the end of long or short branches.

A class of the fluoroaliphatic sulfinates useful in this invention canbe represented by the following general formulae ##STR1## wherein R_(f)represents a monovalent fluoroaliphatic radical having, for example,from 1 to 20 carbon atoms, preferably 4 to 10 carbon atoms, R_(f),represents a polyvalent, preferably divalent, fluoroaliphatic radicalhaving, for example, from 1 to 20 carbon atoms, preferably from 2 to 10carbon at oms, M represents a hydrogen atom or cation with valence x,which is 1 to 2, and is preferably 1, n is 1 to 4, preferably 1 or 2.

The monovalent fluoroaliphatic radical, R_(f), is a fluorinated, stable,inert, non-polar, saturated moiety. It can be straight chain, branchedchain, and, if sufficiently large, cyclic, or combinations thereof, suchas alkyl cycloaliphatic radicals. Generally, R_(f) will have 1 to 20carbon atoms, preferably 4 to 10, and will contain 40 to 83 weightpercent, preferably 50 to 78 weight percent fluorine. The preferredcompounds are those in which the Rf group is fully or substantiallycompletely fluorinated, as in the case where R_(f) is perfluoroalkyl,C_(n) F_(2n+1), where n is 1 to 20.

The polyvalent, preferably divalent, fluoroaliphatic radical, R_(f) is afluorinated, stable, inert, non-polar, saturated moiety. It can bestraight chain, branched chain, and, if sufficiently large, cyclic orcombinations thereof, such as alkylcycloaliphatic diradicals. Generally,R_(f) ', will have 1 to 20 carbon atoms, preferably 2 to 10. Thepreferred compounds are those in which the R_(f), group isperfluoroalkylene, C_(n) F_(2n), where n is 1 to 20, orperfluorocycloalkyl, C_(n) F_(2n), where n is 5 to 20.

With respect to either R_(f) or R_(f) ', the skeletal chain of carbonatoms can be interrupted by divalent oxygen, hexavalent sulfur ortrivalent nitrogen hetero atoms, each of which is bonded only to carbonatoms, but preferably where such hetero atoms are present, such skeletalchain does not contain more than one said hetero atom for every twocarbon atoms. An occasional carbon-bonded hydrogen atom, iodine,bromine, or chlorine atom may be present; where present, however, theypreferably are present not more than one for every two carbon atoms inthe chain. Where R_(f) or R_(f) '0 is or contains a cyclic structure,such structure preferably has 6 ring member atoms, 1 or 2 of which canbe said hetero atoms, e.g., oxygen and/or nitrogen. Examples of R_(f)radicals are fluorinated alkyl, e.g., C₄ F₉₋₋, C₆ F₁₃ --,C₈ F₁₇ --,alkoxyalkyl, e.g., C₃ F₇ OCF₂ --. Examples of R_(f) ' are fluorinatedalkylene, e.g., --C₄ F₈ --, --C₈ F.sub. 16 --. Where R_(f) is designatedas a specific radical, e.g., C₈ F₁₇ --, it should be understood thatthis radical can represent an average structure of a mixture, e.g., C₆F₁₃ -- to C₁₀ F₂₁ --, which mixture can also include branchedstructures.

Representative fluoroaliphatic sulfinate compounds useful in thepractice of this invention include the following:

CF₃ SO₂ Na

C₄ F₉ SO₂ H

C₈ F₁₇ SO₂ Na

CF₃ C(Cl)₂ CF₂ SO₂ K

Cl(CF₂)₈ OC₂ F₄ SO₂ Na

Cl(CF₂)₈ CF₂ SO₂ Na, where x is 0,1,3,4,7,9

NaO₂ SC₈ F₁₆ SO₂ Na

NaO₂ SC₆ F₁₂ SO₂ Na

NaO₂ SC₂ F₄ OC₂ F₄ SO₂ Na

NaO₂ SC₂ F₄ OC₂ F₄ X, where X is Br or I

NaO₂ S[C₄ F₈ O]_(n) C₃ F₆ SO₂ Na

NaO₂ SCF₂ O(CF₂ CF₂ O)_(m) (CF₂ O)_(n) CF₂ SO₂ Na

(CF₃)₂ NCF₂ CF₂ SO₂ Na

(C₂ F₅)₂ NCF₂ CF₂ SO₂ Na

N(C₂ F₄ SO₂ Na)₃

NaO₂ SC₈ F₁₆ SO₂ F ##STR2## NaO₂ SC₃ F₆ O(C₄ F₈ O)_(n) C₃ F₆ SO₂ Nawhere n is 4 to 8.

Suitable fluorine-containing ethylenically-unsaturated monomers for usein the method of this invention include the terminally unsaturatedmonoolefins typically used for the preparation of fluorine-containingpolymers such as vinylidene fluoride, hexafluoropropene,chlorotrifluoroethylene, 2-chloropentafluoropropene, perfluoroalkylvinyl ethers, e.g., CF₃ OCF=CF₂ or CF₃ CF₂ OCF=CF₂, tetrafluoroethylene,1-hydropentafluoropropene, 2-hydropentafluoropropene,dichlorodifluoroethylene, trifluoroethylene, 1,1-dichlorofluoroethylene,vinyl fluoride, and mixtures thereof. Perfluoro-1,3-dioxoles such as##STR3## may also be used. The perfluoro-1,3-dioxole monomers and theircopolymers are described, for example, in U.S. Pat. No. 4,558,141(Squire). Certain fluorine-containing di-olefins are also useful, suchas, perfluorodiallylether and perfluoro-1,3-butadiene. Saidfluorine-containing monomer, or fluoromonomer, may also be copolymerizedwith fluorine-free terminally unsaturated monoolefin comonomers, e.g.,ethylene or propylene. Preferably at least 5% by weight, most preferablyat least 50%, of all monomers in said polymerizable mixture arefluorine-containing. Said fluorine-containing monomer may also becopolymerized with iodine- or bromine-containing cure-site comonomers inorder to prepare peroxide curable polymers, e.g., fluoroelastomers.Suitable cure-site monomers include terminally unsaturated monoolefinsof 2 to 4 carbon atoms such as bromodifluoroethylene,bromotrifluoroethylene, iodotrifluoroethylene, and4-bromo-3,3,4,4-tetrafluorobutene-1. Preferably, all or essentially allof the comonomers in said polymerizable mixture are ethylenicallyunsaturated monomers.

The method of this invention can comprise the use of perfluorosulfinatein otherwise conventional free-radical polymerization. Such conventionalpolymerization includes free-radical polymerization of monomers alone oras solutions, emulsions, or dispersions in an organic solvent or water.Polymerization in an aqueous emulsion or suspension is often preferredbecause of the rapid and nearly complete conversion of monomers, easyremoval of the heat of polymerization, and ready isolation of thepolymer. Emulsion or suspension polymerization typically involvespolymerizing monomers in an aqueous medium in the presence of aninorganic free-radical initiator system and surfactant or suspendingagent.

In one aspect, the method of this invention comprises the use offluorinated sulfinate as a reducing agent and a water soluble oxidizingagent capable of converting the sulfinate to a sulfonyl radical.Preferred oxidizing agents are sodium, potassium, and ammoniumpersulfates, perphosphates, perborates, and percarbonates. Particularlypreferred oxidizing agents are sodium, potassium, and ammoniumpersulfates. The sulfonyl radical so produced is believed to eliminateSO₂, forming a fluorinated radical that initiates the polymerization ofthe ethylenically unsaturated monomers.

In addition to the sulfinate, other reducing agents can be present, suchas sodium, potassium or ammonium sulfites, bisulfite, metabisulfite,hyposulfite, thiosulfite, phosphite, sodium or potassium formaldehydesulfoxylate or hypophosphite. Activators such as ferrous, cuprous, andsilver salts, may also be present.

Aqueous emulsions can be carried out under conventional steady-stateconditions in which, for example, monomers, water, surfactants, buffersand catalysts are fed continuously to a stirred reactor under optimumpressure and temperature conditions while the resulting emulsion orsuspension is removed continuously. An alternative technique is batch orsemibatch polymerization by feeding the ingredients into a stirredreactor and allowing them to react at a set temperature for a specifiedlength of time or by charging ingredients into the reactor and feedingthe monomer into the reactor to maintain a constant pressure until adesired amount of polymer is formed.

The amount of fluoroaliphatic sulfinate used can vary, depending, forexample, on the molecular weight of polymer desired. Preferably theamount of fluoroaliphatic sulfinate is from 0.01 to 50 mole %, and mostpreferably from 0.05 to 10 mole %, of sulfinate compound based on totalquantity of monomers.

Combinations of monosulfinates, disulfinates, and trisulfinates can beused, depending on whether it is desired to use sulfinate as aninitiator, a monomer, or both. When polyvalent sulfinates, such as thoserepresented by Formula II, are used, the sulfinate is a monomer and thefluorinated moiety is incorporated into the polymer backbone. Whenmonosulfinates are used the fluorinated moiety is incorporated as apolymer end group.

Polymers prepared by the method of this invention, such asfluoroelastomer gums, can be compounded and cured using conventionalmethods. Such polymers are often cured by nucleophiles such as diaminesor polyhydroxy compounds. For example, the fluoroelastomers of thisinvention may be crosslinked with aromatic polyhydroxy compounds, suchas bisphenols, which are compounded with the polymer along with a curingaccelerator, such as a quaternary phosphonium salt, and acid acceptors,such as magnesium oxide and calcium hydroxide. Particularly usefulpolyhydroxy compounds include 4,4'-thiodiphenol,isopropylidene-bis(4-hydroxybenzene), andhexafluoroisopropylidene-bis(4-hydroxybenzene) ("bisphenol AF") whichare described, for example, in U.S. Pat. No. 4,233,421 (Worm). Suchcrosslinking methods are described, for example, in U.S. Pat. Nos.4,287,320 (Kolb), 4,882,390 (Grootaert et al.), 5,086,123 (Guenthner etal.), and Canadian patent 2056692 (Kruger et al.).

Certain polymers may be cured with peroxides. A cure-site monomersusceptible to free-radical attack is generally required to renderpolymers peroxide-curable. For example, polymers which containinterpolymerized units derived from iodine- or bromine-containingmonomers are often peroxide-curable. Such cure-site monomers aredescribed, for example, in U.S. Pat. Nos. 4,035,565 (Apotheker et al.),4,450,263 (West), 4,564,662 (Albin), and Canadian Pat. application No.2,056,692 (Kruger et al.)

The polymers of this invention can also be compounded with processingagents, such as those conventionally used to aid in the molding orextrusion of the formulation, e.g. carnauba wax or dichlorodiphenylsulfones and other diorgano sulfur oxides, such as those described inU.S. Pat. No. 4,287,320 (Kolb).

Fillers can be mixed with the polymers of this invention to improvemolding characteristics and other properties. When a filler is employed,it can be added in amounts of up to about 100 parts per hundred parts byweight of polymer, preferably between about 15 to 50 parts per hundredparts by weight of the polymer. Examples of fillers which may be usedare thermal-grade carbon blacks, or fillers of relatively lowreinforcement characteristics such as clays and barytes.

The sulfinate compounds useful in this invention result in polymerswhich have non-polar, non-ionic end groups. These non-ionic end groupsgenerally result in improved properties such as improved thermalstability and improved rheological behavior. Polymers with non-ionic endgroups exhibit lower apparent viscosities during processing, e.g.injection molding, when compared at the same shear rates to polymerswith ionic end groups. The resulting polymers may be elastomers orplastics. The polymers may be shaped to form useful articles including0-rings, fuel-line hoses, shaft seals, and wire insulation.

When disulfinates are used in the polymerization method of thisinvention, diradicals are formed that are incorporated in the polymerbackbone. This method can be used to prepare a variety of new polymerswith new microstructures which would otherwise be inaccessible.

The polymers of this invention can be mixed with other polymers, forexample, with polymers of higher or lower molecular weight to give abimodal molecular-weight mixture. For example, low molecular-weightpolymers of this invention can be mixed with conventionalfluorine-containing polymers to improve the processing characteristicsthereof.

EXAMPLE

The cure characteristics and rheological properties of uncuredcompositions were obtained using ASTM test method D 2084-75 with nopreheat, an oscillator frequency of 100 cpm and a 3° arc, at 177° C.Minimum torque (M_(L)), highest torque attained during a specifiedperiod of time when no plateau or maximum torque is obtained M_(H)),time for torque to increase 0.2 N.m above M_(L) (t_(s) 2), and time fortorque to reach M_(L) =0.9 M_(H) -0.9 M_(L) (t_(c) '(90)) weredetermined. The results are shown in Table 2.

Compounded polymer compositions were press-cured for 10 min. at 177° C.and post-cured for 16 hours at 230° C. and physical propertiesdetermined. Tensile strength at break, elongation at break, and modulusat 100% elongation were obtained using ASTM Method D-412-80 on a samplecut from 1.8 mm sheet of cured polymer with ASTM Die D. Hardness (ShoreA-2) was measured at room temperature on cured samples according to ASTMMethod D-2240-81 using Shore Instrument and Mfg. Co. "A-2" hardnessmeasuring device. Compression set was determined using ASTM MethodD-395-78, Method B, on cured (10 min. press cure at 177° C. followed by16 hours postcure at 230° C.) O-rings after 25% compression for 70 hoursat 200° C. Compression set results are reported as percent of thecompression remaining.

The following Examples describe the preparation of perfluoroalkylsulfinates and their use as free radical initiators in thepolymerization of fluorine-containing monomers to prepare fluoropolymersof the invention containing perfluoroalkyl end groups orperfluoroalkylene chain segments.

Preparation of Sulfinates

The fluorochemical sulfinates C₈ F₁₇ SO₂ Na and (CF₂)₆ (SO₂ Na)₂ ("FS-1"and "FS-2") were prepared by deiodosulfination of the correspondingiodides (C₈ F₁₇ I and I(CF₂)₆ I) with Na₂ S₂ O₄ following the generalprocedure of Hu et al. in J. Org. Chem., Vol. 56, No. 8, 1991, page2803.

The fluorochemical sulfinate C₄ F₉ SO₂ H ("FS-3") was prepared byreduction of the corresponding sulfonyl fluoride C₄ F₉ SO₂ F with Na₂SO₃. The purity of these fluorochemical sulfinates, as determined by ¹⁹F NMR anylysis, was about 90%. (About 9% of HCF₂ C₇ F₁₄ SO₂ Na waspresent in FS-1.)

Fluorochemical sulfinate N,N-bis(2-sulfinotetrafluoroethyl)perfluoropiperazine ("FS-4"), was prepared byreduction of N,N'-bis[2-(fluorosulfonyl)ethyl]piperazine, m.p. 73° C.,with NaBH₄ in tetrahydrofuran (THF) solution. The solid reactionproduct, obtained on evaporation of the THF, was dissolved in 10%aqueous sulfuric acid and the sulfinic acid product, FS-4, was recoveredby eXtraction with diethyl ether. ¹⁹ F NMR analysis of the sulfinicacid, m.p. 115° C. dec., indicated 97% purity. The N,N'-bis[2-(fluorosulfonyl)ethyl]piperazine was prepared by the addition of 2moles of vinylsulfonylfluoride to piperazine followed by electrochemicalfluorination of the resulting adduct.

Preparation of Polymers

Several fluoropolymers were prepared using the above fluorochemicalmono- and disulfinates. Aqueous emulsion polymerization utilizing thesesulfinates were carried out with the following monomers: vinylidinefluoride (VF₂, CH₂ =CF₂), hexafluoropropylene (HFP, CF₃ CF=CF₂),tetrafluoroethylene (TFE, CF₂ =CF₂), bromodifluoroethylene cure sitemonomer (BDFE, CF₂ =CHBr), and chlorotrifluoroethylene (CTFE).

EXAMPLE 1

A 4-L stainless steel high pressure reactor was charged with 2.8 L ofdeionized water, 12 g of K₂ HPO₄, 4 g of (NH₄)₂ S₂ O₈ and 9 g of FS-1(C₈ F₁₇ SO₂ Na). The reactor was evacuated (vacuum pump) and thenpressurized with nitrogen to 0.17 MPa (25 psig). This evacuation andpressurization was repeated four consecutive times. The reactor andcontents were then heated to 71° C. and pressurized to 0.90 MPa (130psig) with a mixture of VF2(61.7 weight %) and HFP (38.3 weight %). Thereactor contents were agitated (650 rpm) and pressure maintained at 0.90MPa with the monomer mixture as the monomers were consumed in thepolymerization reaction. After a period of three hours, during which atotal of 860 g of the monomer mixture was used, the reactor was cooledto room temperature.

Excess monomer was vented and the reactor drained. A portion of thewhite latex (2.5 kg) was added slowly to a solution of 18 g of MgCl₂.6H₂O in 800 g of water and 25 g of n-butyl alcohol. The white rubberypolymer which precipitated was washed several times with hot deionizedwater and dried overnight in a circulating air oven at 100°-120° C. ¹⁹ FNMR analysis of the polymer (in perdeutero acetone solution, CFCl₃reference) showed resonances at -80.5 ppm (CF₃) and -120 to -126 ppm(CF₂), supporting the presence of a C₈ F₁₇ end group in the polymer.Further analysis showed the presence of (in relative mole %) polymerunits derived from 78.37% VF2, 20.98% HFP, and the following end groups:0.10% C₈ F₁₇, 0.46% HCF₂ and 0.09% CH₃ CF₂. A FT IR spectrum of a thickfilm, revealed no absorptions between 1500 and 2000 cm⁻¹, while acomparative VF2/HFP copolymer (Cl above), prepared without thefluorochemical sulfinate, had absorption peaks at 1714 and 1753cm⁻¹indicating polar (carbonyl) end groups.

COMPARATIVE EXAMPLE CL

Comparative Example Cl is a copolymer of VF₂ and HFP (about 80/20 mole %ratio) prepared using conventional emulsion polymerization recipes asdescribed in Ex. 1, without fluorochemical sulfinate.

EXAMPLE 2

The polymerization described in Example 1 was repeated with 1/2 of thequantity of initiators and with the addition of a fluorochemicalemulsifier. Thus, 2.8L of deionized water, 12 g of K₂ HPO₄, 2 g of(NH₄)₂ S₂ O₈ and 4.5 g of FS-1 (C₈ F₁₇ SO₂ Na) and 0.6 g of C₈ F₁₇ SO₂N(C₂ H₅)CH₂ COOK emulsifier were charged to the 4 L reactor. Followingthe same procedure as in Ex. 1, a total of 870 g of monomer mixture waspolymerized. The polymerization took five hours and twenty minutes.Analytical data obtained on the resulting polymer supported the presenceof C₈ F₁₇ end groups.

EXAMPLE 3

The fluorochemical sulfinic acid, FS-3, C₄ F₉ SO₂ H, was employed inthis polymerization. It was first converted to the sodium salt, C₄ F₉SO₂ Na, by dissolving 5 g of the sulfinic acid in 100 mL deionized waterand adding 0.7 g of NaOH followed by 2 g of K₂ HPO₄. This solution wasadded to 2.8L of deionized water containing 10 g of K₂ HPO₄, 4 g of(NH₄)₂ S₂ O₈ and 0.6 g of C₈ F₁₇ SO₂ N(C₂ H₅)CH₂ COOK emulsifier. Thesolution was added to the high pressure reactor and 1000 g of the samemonomer blend used in Example 1 polymerized at a pressure of 0.79 MPa(115 psig) at 71° C. over a period of 4 hours. A portion of theresulting latex (2.0kg) was coagulated and the white, rubbery polymerproduct isolated, washed and dried as described in Ex 1. The Mooneyviscosity of the rubber (ML 1+10@121° C.) was 71. ¹⁹ F NMR analysisshowed resonances at -80.9, -123.9 and -125.5 ppm, supporting thepresence of the C₄ F₉ end group in the polymer chains.

EXAMPLE 4

Example 3 was repeated except that a different monomer mixture was used.950 g of a monomer mixture from an 8L high pressure cylinder containinga mixture of 59.4 weight % VF₂, 40.3 % HFP and 0.40 % BDFE cure sitemonomer. The monomer blend was polymerized over a period of 6.5 hours ata pressure of 0.79 MPa (115 psig) at 71° C. A portion of the resultinglatex was coagulated and the white polymer product was washed and driedas described in Example 1. The polymer had a Mooney Viscosity ((ML1+10@121° C.) of 61. ¹⁹ F NMR analysis supported the presence of the C4F9end groups in the polymer. The polymer contained 0.18 wt. % bromine asdetermined by X-ray fluorescence.

EXAMPLE 5

This Example describes the preparation of a fluoropolymer of VF₂, HFPand TFE using the sulfinate FS-1.

An 86-L high pressure reactor was charged with deionized water (45 kg),K₂ HPO₄ (160.7 g), C₈ F₁₇ SO₂ Na (143.2 g), (NH₄)₂ S₂ O₈ (64 g) andCsF17SO₂ N(C₂ H₅)CH₂ COOK (9.6 g) emulsifier. After 4 consecutive vacuumand nitrogen purge cycles, the reactor was pressurized to 0.76 MPa (110psig) at 71° C. with 384 g VF₂, 853 g HFP and 175 g of TFE. Agitation(130 rpm) was started and as soon as a pressure drop occurred, the 3monomers were added at a rate to maintain constant pressure with thefollowing monomer composition: 44.9 wt. % VF₂, 31.5% HFP and 23.6% TFE.After a total of 15.76 kg of monomers had reacted, the monomer supplywas stopped and the reaction continued until the pressure decreased to0.43 MPa (61 psig). At this point, the reactor and contents were cooledto room temperature and unreacted monomers vented. The reactor was thendrained and the latex polymer product was coagulated and the white,rubbery polymer product washed and dried as described in Ex. 1. Thepolymer had a Mooney viscosity (ML 1+10 @121° C.) of 69 and acomposition (by ¹⁹ F NMR analysis) of polymer units derived from 41.8wt% VF₂, 32.8% HFP and 25.2% TFE, and with 0.23% C₈ F₁₇ end groups.

EXAMPLE 6

This Example describes the preparation of a fluoropolymer of VF2 and HFPusing a disulfinate as an initiator.

To a 4L stainless steel high pressure reactor was charged 2.8L deionizedwater, 12 g of K₂ HPO₄ and 2 g of (NH₄)₂ S₂ O₈. The reactor wasevacuated and the vacuum broken with nitrogen, and this cycle repeated 4times. Then a solution of 4.2 g of the fluorochemical disulfinate FS-2,(CF₂)₆ (SO₂ Na)₂, in 100 mL water was charged together with a solutionof 0.6 g of C₈ F₁₇ SO₂ N(C₂ H₅)CH₂ COOK emulsifier in 100 mL of water.The reactor was pressurized to 0.90 MPa (130 psig) at 71° C. with amonomer blend of 61.7 wt. % VF₂ and 38.3% HFP. The reactor contents werestirred (600 rpm) and the polymerization continued for 6 hours until atotal of 360 g of monomers was polymerized. The resulting polymer latexwas coagulated and the white, rubbery polymer product washed and driedas described in Ex. 1 A ¹⁹ F NMR analysis showed resonances in theregion -119 to -123 ppm (CFCl₃ standard) indicative of --CF₂ (CF₂)_(x)CF₂ --units in the polymer backbone, calculated to be a level of about0.06 mole % of --(CF₂)₆ -units based on total moles of interpolymerizedunits.

EXAMPLE 7

This Example describes the preparation of a fluoropolymer of VF₂ and HFPusing another disulfinate as an initiator.

Example 6 was repeated except that in place of the FS-2 sulfinate, 4.9 gof FS-4 was used, after conversion to the sodium salt, NaO₂ SC₂ F₄ N(CF₂CF₂)₂ NC₂ F₄ SO₂ Na, with aqueous sodium hydroxide. The reactor waspressurized to 0.90 MPa (130 psig) at 71° C. with a monomer blend of61.7 wt. % VF₂ and 38.3% HFP. The reactor contents were stirred (600rpm) and the polymerization continued for 4.5 hours until a total of 780g of monomers was polymerized. The resulting polymer latex wascoagulated and the white, rubbery polymer product washed and dried asdescribed in Ex. 1. ¹⁹ F NMR analysis (in perdeuterated DMF solvent)showed ressonances due to CF₂ --N--CF₂ -- at -90.7 ppm supporting thepresence of the --C₂ F₄ N(CF₂ CF₂)₂ NC₂ F₄ -- unit in the polymerbackbone.

EXAMPLE 8

This Example describes the preparation at room temperature of afluoroplastic, polychlorotrifluoroethylene by the polymerization ofchlorotrifluoroethylene (CTFE) in the presence of a fluorochemicalsulfinate.

In a 4L high pressure reactor was placed 3.44 kg of deionized water,22.6 g Na₂ HPO₄, 19.3 g of C₇ F₁₅ COONH₄ emulsifier and 16.0 g of C₈ F₁₇SO₂ Na. After successive evacuations with a vacuum pump and pressurizingwith nitrogen followed by a final evacuation, the reactor contents werestirred at 750 rpm and heated to 27° C. at a pressure of 0.0048 MPa (0.7psig). Then 20.7 g of a 35 wt. % aqueous solution of (NH₄)₂ S₂ O₈ wereadded concurrently with 1,000 g of CTFE over 3 hours at 26° C. Thereactor pressure increased from 0.0048 MPa (0.7 psig) to 0.72 MPa (104psig) over this period. The reactor was held at a temperature of about26° C. for 62 hours during which time the pressure fell to 0.12 MPa (17psig). The reactor was cooled to room temperature and the product, awhite emulsion, was drained and freeze-coagulated overnight to yield aflaky, white solid which was collected by aspirator suction on a linencloth and washed 7 times with a 77 wt % water and 23 wt % methanolsolution. ¹⁹ F NMR analysis supported the presence of C₈ F₁₇ end groupsin the polymer.

EXAMPLE 9

This example describes the preparation of a fluoropolymer of VF2 and HFPat room temperature using a combination of perfluoroalkyl sulfinate(FS-1), C₈ F₁₇ SO₂ Na, and potassium sulfite, K₂ SO₃, as reducingagents.

To a 4-L high pressure reactor was 2.8 L deionized water, 12 g K₂ HPO₄,9g C₈ F₁₇ SO₂ Na, 0.09 g CuSO₄.5 H₂ O, 0.6 g of C₈ F17SO₂ N(C₂ H₅)CH₂COOK emulsifier and 7.5 g of (NH₄)₂ S₂ O₈. The reactor was pressurizedwith a blend of 61.7 wt % VF2 and 38.3 wt % HFP to a pressure of 0.83MPa (120 psig) at 15° C. Agitation (500 rpm) was commenced and a 5 wt %solution of K₂ SO₃ was fed to the reactor. After 30 g of this solutionhad been added, a drop in pressure was noted indicating thatpolymerization was taking place. The monomer mixture was fed to thereactor at a rate to maintain the pressure at 0.83 MPa (120 psig), alongwith potassium sulfite solution at a rate of 20 g hr⁻¹. After 3.5 hours,a total of 1.02 kg of the monomer mixture had been consumed and a totalof 70 g of potassium sulfite solution used. The excess monomer mixturewas vented and the reactor drained and the resulting latex coagulatedand the white, rubbery polymer product washed and dried as described inEx. 1. The polymer had a Mooney viscosity (ML 1+10@121° C.) of 53 and acomposition (by ¹⁹ F NMR analysis) of polymer units derived from 61.2 wt% VF₂ and 38.3 wt % HFP and with 0.5 wt % C₈ F₁₇ end groups.

This example demonstrates that a perfluorinated radical is formed evenin the presence of a competing reducing agent such as potassium sulfite.Thus, the perfluorinated sulfinates of this invention can be used incombination with sulfites and other known reducing agents.

Curing of Fluoroelastomers

In the following Examples and Comparative Examples, polymers were curedand tested.

Three of the fluoropolymers of this invention (polymers of Examples 1, 4and 5), containing perfluoroalkyl end groups, were cured. The curerheology and cure properties are compared with analagous, ComparativeExamples C2, C3 and C4, wherein the fluoropolymers used were preparedwith the same monomers but in the absence of fluorochemical sulfinates.The cure compositions and cure rheology and other physical propertiesare shown in Tables 1 and 2 below.

EXAMPLE 10

The fluoroelastomer gum prepared in Example 5 was compounded with 30 phrMT black, 6 phr Ca(OH)₂, 3 phr MgO, and cured with 3.5 millimoles per100 g of resin (mmhr) bisphenol AF, and 1.27 mmhr of phosphonium cureaccelerator, [(C₄ H₉)₃ P⁺ CH₂ CH₃ ][⁻ OC₆ H₄ C(CF₃)₂ --C₆ H₄ -OH]prepared from the reaction of tributyl (2-methoxypropyl) phosphoniumchloride and the sodium salt of hexafluoroisopropylidenebis(4-hydroxybenzene).

COMPARATIVE EXAMPLE C2

A fluoroelastomer gum was prepared as in Example 5 except without C₈ F₁₇SO₂ Na. The resulting gum was cured and tested as in Example 10.

EXAMPLE 11

The fluoroelastomer gum of Example 4 was cured and tested as in Example10 except with 3 phr of Ca(OH)₂, 2.5 phr of triallylisocyanurate (TIAC),and 2.5 phr Luperco 101 XL organic peroxide from Atochem, and withoutMgO, bisphenol AF, and phosphonium cure accelerator.

COMPARATIVE EXAMPLE C3

A fluoroelastomer gum was prepared as in Example 4 except with 0.4weight % BDFE and without C₄ F₉ SO₂ Na. The resulting gum was cured andtested as in Example 11. The polymer contained 0.25 wt. % bromine asdetermined by X-ray fluorescence.

EXAMPLE 12

The fluoroelastomer gum of Example 1 was cured and tested as in Example10.

COMPARATIVE EXAMPLE C4

A fluoroelastomer gum was prepared as in Example 1 except without C₈ F₁₇SO₂ Na. The resulting gum was cured and tested as in Example 10.

                  TABLE 1                                                         ______________________________________                                        Example   C2     10       C3   11     C4   12                                 Rheology Data Rheometer 177° C., 3° arc, 100                    ______________________________________                                        cpm                                                                           M.sub.L, N.m                                                                            1.13   1.80     2.03 1.24   1.24 1.70                               t.sub.s 2 (minutes)                                                                     2      1.9      1.2  1.4    1.1  1.2                                t.sub.c ' (50)                                                                          2.8    2.8      2.3  2.5    1.6  1.8                                (minutes)                                                                     t.sub.c ' (90)                                                                          3.1    3.1      5.1  5.5    1.8  2.0                                (minutes)                                                                     M.sub.H, N.m                                                                            7.91   9.15     8.70 4.75   10.4 10.4                               ΔTorque                                                                           6.78   7.35     6.67 3.51   9.16 8.70                               (M.sub.H -M.sub.L)                                                            ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Cured Properties Press cure 10 min. @ 177° C. & post                   cure 16 hrs @ 230° C.                                                  Tensile, MPa                                                                           11.9    13.3    16.7  13.4  15.6  16.1                               Elongation,                                                                            270     285     241   336   197   213                                100%     4.97    4.00    4.08  2.88  5.54  5.29                               modulus                                                                       Hardness 80      75      71    68    74    74                                 (Shore A2)                                                                    Compression Set                                                               O-rings, 70                                                                            39.5    24.3    34.6  48.1  21.0  20.7                               hrs @ 200° C.                                                          Heat-aged dumbbells (70 hrs @ 275° C.)                                 Tensile, MPa                                                                           4.00    6.93                                                         Elongation,                                                                            445     370                                                          %                                                                             100%     2.00    2.03                                                         modulus                                                                       Hardness 80      72                                                           (Shore A2)                                                                    ______________________________________                                    

The data in Tables 1 and 2 show that the polymers of this invention arereadily cured with either a bisphenol (Examples 10 and 11) or a peroxide(Example 11) cure system, giving good physical properties. Inparticular, Example 10 illustrates (compared with Comparative ExampleC2) that cured polymers of this invention have improved properties,e.g., compression set resistance, and better retention of physicalproperties after heat aging compared to fluoroelastomers prepared byconventional methods.

Various modification and alterations of this invention will be apparentto those skilled in the art without departing from the scope and spiritof this invention and this invention should not be restricted to thatset forth herein for illustrative purposes.

What is claimed is:
 1. A method for the preparation offluorine-containing polymer comprising, polymerizing, under free-radicalconditions, an aqueous emulsion or suspension of a polymerizable mixturecomprising a fluoroaliphatic-radical containing sulfinate, and anoxidizing agent capable of oxidizing said sulfinate to a sulfonylradical.
 2. The method of claim 1 wherein said polymerizable mixturefurther comprises fluorine-containing ethylenically unsaturated monomer.3. The method of claim 2 wherein said fluorine-containing monomer isselected from the group consisting of vinylidene fluoride,hexafluoropropene, chlorotrifluoroethylene, 1-chloropentafluoropropene,perfluoroalkyl vinyl ethers, tetrafluoroethylene,1-hydropentafluoropropene, dichlorodifluoroethylene,2-hydropentafluoropropene, vinyl fluoride, trifluoroethylene,1,1-dichlorofluoroethylene, perfluorodiallylether, andperfluoro-1,3-dioxoles.
 4. The method of claim 1 wherein saidpolymerizable mixture further comprises fluorine-free ehtylenicallyunsaturated monomer.
 5. The method of claim 1 wherein said oxidizingagent is water-soluble.
 6. The method of claim 1 wherein said oxidizingagent is selected from the group consisting of sodium, potassium, andammonium persulfates.
 7. The method of claim 1 wherein said sulfinate isR_(f) (SO₂ M_(1/x))_(n) where R_(f) is fluoroaliphatic radical, M is ahydrogen atom or a cation of valence x, and n is 1 or 2.